Light emitting elements comprising Light Emitting Diode (LED) packages incorporated in glass are currently fabricated for architectural purposes. In these elements, two-dimensional LED arrays are sandwiched between two glass plates laminated by a polymer, usually PVB (polyvinylbutyral). The LED packages are fixed on one glass plate on which a pattern of conductors is present to provide the current for the LED packages. The above construction is beneficial since it imparts durability to the construction, so that the field of use increases.
A problem that is present for LEDs fully immersed in a glass like medium is that total internal reflection (TIR) occurs at the interface between the glass surface and the surrounding air. A consequence is that light with angles larger than the critical angle is totally reflected at the glass/air interface, resulting in an optical efficiency of about 41%. The totally reflected light is absorbed in the glass/PVB/glass system (after multiple internal reflections). A further problem is that the brightness of LED packages is high (1-10 MCd/m2), which results in that for instance glass walls incorporating LED packages exhibit a low visual comfort with multiple glaring light sources. Furthermore, commercially available top-emitting LED packages are typically quite thick (>0.8 mm), and consequently the PVB layer needs to be thick. This results in an increased cost and contributes to a brownish color of the glass structure, due to the optical properties of PVB. In the case of an isolated LED packages in a large glass stack all totally reflected light is finally absorbed. In addition, at relatively high LED package densities (e.g. >0.5 cm−2) totally reflected light could scatter at neighboring packages, leading to unpredictable light outcoupling.
The present invention aims at alleviating the above drawbacks in prior art systems.